1. Field of Invention
The present invention relates generally to safety brakes for hydraulic jacks or rams. In particular the present invention relates to a hydraulic ram lifting elevator emergency arrestor using a lever and lock mechanism to provide braking action without permanently damaging or destroying the hydraulic ram.
2. Description of the Prior Art
The present invention relates to a hydraulic ram arrestor using a lever lock type of mechanism which is activated by a pressure failure condition, down overspeed, or uncontrolled down motion. When activated, two lever acting brake arms are dropped into contact with the elevator ram, the resulting friction bringing the elevator to a sliding stop.
There have been numerous brake systems developed for stopping hydraulic ram elevators during emergency situations. All of the prior art patents found were directed toward collets or brake shoes, that, during a hydraulic pressure failure, would drop down and wedge in between a fixed housing and the ram of the elevator. The friction generated by the downward motion of the ram in contact with the collet or brake shoe causes the collet or brake shoe to be driven downwardly, thereby wedging the ram to a halt. Empirical evidence indicates that the force necessary to stop an elevator using such a brake exceeds the elastic limit of the material used in commercial rams causing the ram to be deformed into an hourglass shape at the point where such brakes grip the ram. This type of damage to the ram cannot be repaired and instead, expensive and time consuming replacement is required to restore the elevator to working condition. The prior art patents also disclosed elevator brakes that have many moving parts, and are correspondingly complex. Additionally, the prior art devices appear relatively large and bulky. Size is an important consideration because there is often limited space into which to fit a braking device. Therefore, it is desirable for the brake to have a low profile, thereby facilitating installation in all present hydraulic elevators.
As a specific example of a prior art design having the above mentioned short comings, Beath et al., U.S. Pat. No. 4,449,615 is a floor mounted lever-actuated wedge device. The many components in this design complicate it by comparison to the present invention. Beath uses collets, that, during a hydraulic pressure failure, drop down and wedge in between a fixed housing and the ram of the elevator. The friction generated by the downward motion of the ram in contact with the collets causes the collets to be driven downward, thereby wedging the ram to a halt. The force necessary to stop an elevator using the brake disclosed in Beath exceeds the elastic limit of the material used in commercial rams causing the ram to be deformed into an hourglass shape at the point where the collets grip the ram. Additionally, the above mentioned patent does not precisely show relation to the top of the cylinder and the bottom of the elevator. However, it appears too tall to fit most existing elevator systems.
In light of the problems listed above and exemplified by U.S. Pat. No. 4,449,615, a new elevator brake is needed that can safely stop a fully loaded elevator without permanently damaging the ram.
The present invention, using an accretable metal or other adherent material to apply a braking force to the ram is a clear improvement over the prior art. Prototype testing has shown that copper bar formed to shape has yielded sufficiently high braking force, with and without the presence of oil on the surface of the ram. Several materials have been tested, and, to date, copper has been the best material for the purpose. The present invention is also comparatively simple and low in profile facilitating installation on current elevator designs.
The general object of the present invention is to provide a mechanism for arresting an elevator which can safely stop a fully loaded elevator without permanently damaging any part of the elevator.
It is another object of the present invention to provide an elevator arrestor that allows the elevator to be usable within a short period of time with little reset and repair necessary. Optimally, the reset and repair should be a relatively simple and inexpensive procedure.
It is a further object of the present invention to provide an arrestor that will fit within a small vertical space such that it can fit within the normal design parameters for hydraulic ram elevators, and may also be retrofit into existing hydraulic ram elevators.
It is yet another object of the present invention to provide a system that can be easily installed and requires very little down time in which the elevator is non-functional.
It is an additional object of the present invention to provide for an arresting system that is inexpensive to manufacture.
The present invention is a hydraulic safety arrestor for slowing and stopping a ram, jack or other cylinder type object. It utilizes two lever acting brake arms lined with an accretable metal as the friction material. When actuated, the brake arms contact the ram circumferentially to slow and stop the falling ram. The lining material is machined inside the brake arms to a diameter slightly less than the diameter of the ram. When actuated, the lining material contacts the ram with sufficient frictional force to stop the downward motion of the ram without deformation of the ram. The rest of the mechanism is comprised of buttress members, pivot pins, and a base plate, mounted above a spacer ring. The spacer ring is the same diameter as the cylinder and is variable in length to raise the base plate and brake assembly above any bolts or other existing projections. Eyelets are welded to the existing cylinder to provide for secure mounting and correct alignment and realignment when the brake is removed and reinstalled.
The brake arms may be actuated mechanically by loss of hydraulic pressure, by an electronic signal from a hydraulic pressure detector, by down overspeed or by an uncontrolled down motion detector.
The force applied by the braking action is transferred from the brake arms through the base plate and spacer ring onto the circumferential area of the top of the main cylinder and any associated support structures. By monitoring the pressure and overspeed, the fall of the elevator can be limited to speeds with a maximum of less than twice the normal down speed, thus limiting the kinetic energy produced, by not allowing a free falling elevator. Therefore, the pit structure would absorb the energy with damage of deformation, without any modifications to the pit structure.